The present invention relates to lens implants or intraocular lenses (IOL's) that are used to replace a patient's natural lens after it has been surgically removed. More particularly, the invention relates to an IOL with a unique haptic or loop configuration that is stiff enough to provide sufficient stability for holding the lens in place after implantation, but is flexible enough to facilitate insertion with no residual negative effects to the patient.
There are many IOL's of varied designs on the market that are used to replace the natural lens after what is known as extra-capsular surgery where the natural lens of the eye is surgically removed. Such lenses include an optical portion or lens and "loops" or "haptics" that retain the optical portion in the eye either anteriorly or posteriorly relative to the iris. The lens that is the subject of the present invention is preferably a posterior chamber, one-piece lens formed of polymethylmethacrylate (e.g., PMMA) or other suitable bio-compatible material, although the same configuration could be used on a three-piece lens where the loops are formed separate from the optic portion and attached to it. In such lenses, the optic portion could be formed of PMMA and the loops of material such as polypropylene.
The optic portion of the lens replaces the natural lens of the eye that has been removed and operates to focus the image discerned by the eye on the retina located on the back wall of the posterior chamber. The loops or haptics project from the periphery of the optic portion and operate to hold the lens in its position within the eye. The degree of flexing and configuration of haptic are important because they determine the characteristics of the loop for holding the IOL in place and also accommodate the constantly changing configuration or shape of the eyeball during the wearer's daily activities.
An IOL is normally inserted through an incision formed by the surgeon at the junction of the corneal and sclera. Various insertion techniques have been developed for minimizing the size of the incision such as, for example, having loops that are flexible enough to be pressed inwardly or by manipulating the loops through the incision and rotating the lens so that the incision need not be any wider than the diameter of the optic portion. The loops are usually in the form of thin, curved arms having a free end. Many IOLs include openings at both ends of the loop or in the outer periphery of the optic portion for accommodating a surgical instrument to aid in implantation.
A number of IOL lens designs have been proposed and used in the past. The acceptability of many of such configurations often times depends on physician preference, but physical characteristics play an important role in determining patient comfort and ease of implantation. One example of a single-piece IOL that has been developed is taught in U.S. Pat. No. 4,476,591 to Arnott, issued Oct. 16, 1984. This lens, while generally similar in design in the subject invention, includes loops that extend well beyond the beginning of the other loop and are believed to be more flexible than desirable. On the other hand, there are lenses such as the one known as the C-loop lens that does not include any portion of the loop spaced radially outward from the periphery of the optic portion and includes loops that terminate far short of the beginning of the next loop and therefore does not provide the flexibility characteristics that many consider to be desirable.
Ideally, the loops or haptics need to provide compressive forces that are great enough to hold a lens in place, but not great enough to exert undue pressure inside the eye. Further, the loops must be stable enough so that as the shape of the eyeball changes, there should be no significant change in lenticular displacement upon compression, nor should descentration (transverse displacement) occur upon compression. Another characteristic is to determine whether the lens tilts in any way during compression.
Balanced against these considerations are whether lenses can be equally locatable within the eye because of the location of positioning holes in similar portions of the lens. Once in the eye, the lens should be able to resist rotational forces within the eye and remain relatively stable throughout the range of changes in the shape of the eyeball. Further, the profile of the lens including the outer periphery of the lens must be considered in order to determine the optimum size of incision for accommodating the lens. Obviously, the larger the required incision the less advantageous the lens.